Projectile base for carrier projectiles

ABSTRACT

In projectile bases (20) for carrier projectiles which are equipped with a cavity (26) on the side facing away from the projectile tail for, for example, a parachute, it may happen that the base plate (23) is axially bent through during firing. This causes the base body (22) to be radially constricted and contact is lost between the rotating band (27) disposed on the body (22) and the gun tube, frequently resulting in a gas breakthrough. To avoid the above-mentioned radial constriction in the region of the rotating band, the projectile base (20) is provided with a base plate (23) which is curved toward the tail of the projectile. The curved configuration of the base plate (23) makes it possible to produce radial widening in the rear projectile base region during firing so as to ensure gas tightness and spin transmission from the rotating band (27) even at high gas pressures.

BACKGROUND OF THE INVENTION

The invention relates to a projectile base for carrier projectilescarrying submunition, with the projectile base including a base bodyhaving a front section with a cylindrical outer surface, a tail sectionwith a conically tapered outer surface and a base plate, a rotating banddisposed on the cylindrical outer surface portion of the base body, andrespective cavities disposed in the respective ends of the base bodywith the base plate therebetween.

Such a projectile base is disclosed, for example in German patent DE No.3,643,291. As tests have shown, such bases exhibit an unfavorabledeformation behavior. This leads to problems in sealing and in thetransmission of spin by the rotating band. The gas breakthrough that isunavoidable at high gas pressures (loss of contact between rotating bandand tube wall) leads to continuous opening and closing of the sealinggap during passage through the tube and thus to the excitation ofoscillations of the projectiles resulting in increased tube wear.

The cause of these sealing problems is that the axial force componentsacting on the tail of the projectile during firing cause the base plateto be axially bent, and is associated with radial widening of the frontprojectile base body and radial constriction of the rear projectile baseand the rear rotating band region. The radial deformation by the axialforce components during firing is superposed on the radial deformationsdue to the simultaneously acting radial force components. Thissuperposition is the cause of the resulting radial deformation of theprojectile base.

The radially acting forces result, on the one hand, from the gaspressure which extends to the rear end of the rotating band and from therotating band pressure. These forces lead to radial constriction of thebase body over its entire length. If, the superposition of bothdeformation states results in radial constriction at the rear edge ofthe rotating band, there will be loss of contact between the rotatingband and the tube. This exposed gap area fills with gas which isequivalent to an increase in the radial force acting on the base body.The result is further enlargement of the radial constriction in therotating band region and finally a complete gas breakthrough.

Furthermore, U.S. Pat. No. 4,327,643 discloses explosive projectileswhose base plates are curved at the tail end. However, the interior ofthe projectiles is filled with an explosive so that the base platecannot be deformed much in the axial and radial directions (if a cavitywere present in the interior of these projectiles, the projectile base,due to its thin walls and the extreme curvature of its base and absentthe radial support by the explosive, would collapse under the gaspressure existing up to the rotating band during firing).

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a projectile baseof the above mentioned type in which radial constriction in the regionof the rotating band is avoided.

This is accomplished according to the invention by providing the surfaceof the base plate which faces the tail of the base with a curvature suchthat this surface is curved and tapers rearwardly toward the projectiletail.

The invention is thus based on the idea that the deformation behaviorduring firing can be corrected by giving the base a curved configurationin that then the axial curvature of the base causes radial widening alsoin the rear projectile base region. This form-specific base deformationduring firing ensures gas tightness and spin transmission from therotating band even under high gas pressures.

U.S. Pat. No. 4,327,643 does not disclose the idea significant for theabove-mentioned invention. In that reference, a corresponding radialconstriction of the rotating band is not to be prevented and does notoccur at all because the projectile itself is filled with explosive downto the base plate.

Details and advantages of the invention will be described below inconnection with embodiments and with the aid of the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are schematic representations, in cross section, of aprior art hollow base at rest and during firing;

FIG. 2 is a schematic cross-sectional view of a hollow base according tothe invention;

FIGS. 3a and 3b, cross-sectional views of a spherical cap base accordingto the invention at rest and during firing;

FIGS. 4a and 4b show a comparison between a prior art flat base with aspherical cap base;

FIG. 5 is a schematic cross-sectional view of the conical base accordingto the invention; and

FIG. 6 is a schematic cross-sectional view of part of a carrierprojectile including the projectile base according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIGS. 1a and 1b, the reference numeral 10 identifies a carrierprojectile hollow cylindrical base composed of a base body 12 having atransversely extending base plate 13 formed therein. Base body 12includes a hollow tail section 14 with an inwardly conically taperedouter surface (also called a boat tail). The reference numeral 15identifies the upper circumferential edge of the tapered surface of thetaper of boat tail 14, i.e. the transition region between the conicaltail section 14 and the cylindrical outer surface of base body 12.

On the side of projectile base 10 facing away from the tail of theprojectile, there is provided an axial cavity 16 in which there are nocomponents to axially support base plate 13 or to radially support thebase body 12. In practice, the parachutes for submunition projectilesdisposed in the carrier projectile are often accommodated in this cavityarea 16. In a conventional manner a rotating band 17 is applied to theouter cylindrical surface of the base body 12. For reasons of clarity,the tube walls of the weapon which contact the band 17 for firing havenot been included in the drawing figures.

In FIG. 1a, the projectile base 10 is shown in its rest position. Asshown in FIG. 1b, the forces acting on the projectile tail during firingcause base plate 13 to be axially bent, this condition being associatedwith radial widening in the front region of base body 12. At the sametime, the tail region of base body 12 is radially constricted, supportedby the pressure from the rotating band 17 and the radially acting gaspressure which is present up to the rear edge of the rotating band 17.This constriction has the result that at high gas pressures rotatingband 17 loses its sealing function relative to the combustion gases fromfiring. Once contact with the rear edge of the rotating band 17 has beenlost, the effect of the radial force is augmented and the radialconstriction of base body 12 increases. A gas breakthrough is thenunavoidable.

FIG. 2 is a cross-sectional view of a projectile base 20 according tothe invention which includes a base body 22 having a base plate 23. Theprojectile base 20 includes a conical tail section 24, circumferentialboat tail edge 25, a cavity accommodating the parachute 26 and arotating band 27. The rear edge of the rotating band 27 is given thereference numeral 28. The base of FIG. 2 is similar to that of FIG. 1awith the exception that the rear surface of the base plate 23, i.e., thesurface facing the tail of the base, is curved so that it tapers towardthe tail and as shown has a convex portion 21 with an outer perimeterportion or edge region 19. The following relationships apply for therearward curvature of base plate 23:

    1/20D≦t≦1/5D

    1/20D≦f≦1/5D

    g≧0

    10°≦β≦40°                 (1)

where

D=caliber of the projectile

t=depth of curvature of the convex portion 21 relative to the outerperimeter portion 19, taken in the axial direction

f=axial distance between the rear edge 28 of the rotating-band 27 andthe outer edge of the curvature

g=distance axial between the rear edge of the rotating band 27 and theupper edge of the boat tail 24

β=maximum pitch angle.

The radial distance between the edge of the convex portion 21 and theinner edge 29 of the boat tail 24; i.e., the width of region 19, issubstantially smaller than the caliber D and essentially corresponds tothe transition radii between the curved portion 21 and the inner surfaceof the boat tail 24. In the following FIGS. 3 to 6, this region 19 isomitted, i.e. the curvature directly follows the inner boat tail edge29.

A projectile base 30 will now be described in greater detail in which acurved portion 31 of a base plate 33 has the shape of a spherical cap.

FIG. 3a shows the projectile base 30 according to the invention in itsrest state. The projectile base 30 has a base body 32, with a base platehaving a spherical cap 31 for a rear surface, and a conical tail sectionor boat tail 34. The boat tail 34 has a circumferential edge 35. Theparachute cavity, the rotating band and the rear edge of the rotatingband are given the reference numerals 36, 37 and 37', 38 and 38'respectively. Instead of Relationship (1), the curvature the convexportion or spherical cap 31 of the base plate 33 can also be describedwith the aid of the following relationship:

    2/3D≦R≦3/2D                                  (2)

where R is the radius of the spherical cap 31.

It must additionally be considered that the following should apply for adistance x between the point of intersection 39 of a mathematicallydefined sphere which contains the outer surface of the extendedspherical cap 31 with the outer cylindrical surface of the body 32 andthe rear edge 38 or 38', respectively, of the rotating band bands 37 or37'.

    x≦1/10D                                             (3)

The point of intersection 39 may here lie in front of or behind therotating band rear edges 38 and 38', respectively. In FIG. 3a, the righthalf of the projectile base 30 shows an embodiment in which the rotatingband edge 38 lies behind the point of intersection 39, while the lefthalf of the projectile base 30 shows an embodiment in which the rotatingband rear edge 38' lies in front of the point of intersection 39'.

In any case, in all embodiments, rotating band rear edges 38 and 38',respectively, must lie in front of the circumferential edge 35 of theboat tail 34 when seen in the direction of flight (g≧0).

The effect of the curved base plate 33 during firing is shown in FIG.3b. Except for part of the conical tail 34, base body 32 is radiallywidened. This ensures gas tightness during firing and also for thetransmission of spin from rotating band 37 or 37', respectively.

FIG. 4 shows the relationships between a projectile base 40' having abase plate 43' with a spherical cap or convex portion 41 according tothe invention (FIG. 4a) and of a conventional flat base 40 having a flatbase plate 43 (FIG. 4b). In both cases, a projectile is involved whichhas a caliber D=155 mm. The length of the projectile bases 40 and 40',position and length of rotating bands 47 and 47', respectively, areidentical. The wall thickness W of the flat base plate 43 is equal tothe greatest wall thickness of the spherical cap base plate 43 and is 30mm. The radius R equals 130 mm. For the flat base 40 the first gasbreakthrough occurred at a pressure of 3600 bar, while for the sphericalcap base 40' gas breakthrough did not occur until a pressure of 4500bar.

FIG. 5 shows as a further example a projectile base 50 according to theinvention having a base plate 53. The base plate has a curved rearsurface 51 which extends toward the tail of the projectile base with aconical taper. The projectile base 50' has a base body 52, and a conicaltail section or boat tail 54 with a circumferential edge 55. similar toFIGS. 3a and 3b, respective points of intersection 59 and 59' of anextension of the conical surface 51 with the cylindrical outer surfaceof the base body 52 may lie in front of or behind the rear edge 58 or58', respectively.

The following relationship applies for the cone angle α of the baseplate 53:

    7°≦α≦25°

Relationship (3) again applies for the distance x between the rear edge58 or 58' of the rotating band and the point of intersection 59 or 59'respectively.

The present invention is particularly advantageous for artillery carrierprojectiles having a thin-walled projectile body. The requirement formaximum length of the useful space limits the height of the base, andthe thin walls of the projectile body require that it be radiallysupported by the base body in the region of the rotating band.

Due to the limited base length, it is thus generally necessary toretract the rotating band rear edge down to the circumferential edge ofthe boat tail (g=0), in order to be able at all to arrange the riflinglength of the rotating band required for the transmission of spin on thetail, that is on the region supported by the base. In order to ensurethe functioning of the entire rotating band with the rotating band rearedge in this position, it is necessary to radially widen the base,coupled with radially squeezing-in of the rotating band in this region.These requirements can be met with the projectile base according to theinvention.

FIG. 6 shows part of a carrier projectile having a thin body. Theprojectile base is marked 60 and is composed of a base body 62 and abase plate 63. Base body 62 includes a conical tail section 64 whoseboat tail edge is marked 65.

One part of a two-part rotating band 67 is seated on base body 62. Thecavity for a parachute (not shown) is marked 66. The thin body 69 of thecarrier projectile is fastened to projectile base 60. Submunition bodiesare disposed in the interior of the carrier projectile. The tail end ofsuch a submunition body is indicated by the reference numeral 70. In apractical embodiment, the base plate 63 includes a curved portion 61which is curved to have the shape of a portion of a sphere.

We claim:
 1. In a carrier projectile, for carrying submunition,comprising a thin walled projectile body which is open at its rear end,a projectile base connected to and closing said rear end of saidprojectile body, and a rotating band disposed on said projectile base,with said projectile base including a cylindrical base body having afront section with a cylindrical outer surface, a tail section with aconically tapered outer surface, and a base plate, with said rotatingband being disposed on said cylindrical outer surface of said base body,with said base plate having a first surface facing a tail end of saidprojectile base and a second surface facing away from said projectilebase tail end, with said first and second surfaces being defined byrespective first and second cavities formed in opposite end surfaces ofsaid base body, and with said second cavity having no componentsdisposed therein to support the said base plate or said base body; theimprovement wherein said first surface of said base plate is curved andtapers toward the longitudinal axis of the projectile base in adirection toward said projectile base tail end such that said basewithstands stresses encountered during firing of said projectile.
 2. Aprojectile according to claim 1, wherein the following relationshipsapply for the curvature of said first surface of said base plate:

    1/20D≦t≦1/5D

    1/20D≦f≦1/5D

    g≧0

    10°≦β≦40°

where D=caliber of the projectile and base plate; t=maximum axial depthof curvature of said first surface; f=axial distance between a rear edgeof said rotating band and an outer edge of the curvature; g=axialdistance between said rear edge of said rotating band and a front edgeof said conically tapered outer surface of said tail section; andβ=maximum pitch angle of said curvature of said base plate.
 3. Aprojectile according to claim 1, wherein said first surface of said baseplate has a curvature with a shape conforming to that of a portion of asphere.
 4. A projectile according to claim 3, wherein said sphere has aradius R, and the following relationship applies for said radius R:

    2/3D≦R≦3/2D

where D is the caliber of the projectile.
 5. A projectile according toclaim 4, wherein the following applies for an axial distance x between arear edge of said rotating band and a point of intersection of a circledescribed by said radius with said outer cylindrical surface of saidbase body:

    x≦1/10D

with said point of intersection lying in front of or behind said rearedge of said rotating band.
 6. A projectile according to claim 1,wherein said first surface of said base plate has a curvature with aconical configuration.
 7. A projectile according to claim 6, wherein thefollowing applies for an axial distance x between a rear edge of saidrotating band and a point of intersection of a mathematically definedcone containing said first surface with said outer cylindrical surfaceof said base body:

    x≦1/10D

with said point of intersection being located in either one of two axialdirections relative to said rear edge of said rotating band.
 8. Aprojectile according to claim 6, wherein the following applies for acone angle α of said first surface of said base plate relative to aradial direction of said base:

    7°≦α≦25°.


9. A projectile as defined in claim 1 wherein said second surface ofsaid base plate is substantially planar.